Femto Access Points (FAPs) usually operate at the same frequency band as the rest of the wireless radio network. Therefore, they create interferences to the external overlaying network (i.e. macro cells) as well as to each other. This is caused by the fact that FAPs are equipped with omni-directional antennas that radiates equal energy at all directions, also in unwanted ones.
Further, the basic principle behind FAPs is that these devices, while being part of the Mobile Operator's Network, are installed at the customers' premises (e.g. at private homes) without any kind of network planning. Therefore, if several FAPs are installed close to each other, the radiation of each may influence the performance of other FAPs using the same radio frequency, as well as the connections to macro base stations established by mobile stations located in the vicinity. This results in degradation of Quality of Service, increase in the transmitted power by the affected mobile stations (which also shortens the battery life) and can lead in extreme cases to the complete blockage of service in affected areas.
FAPs are typically equipped with a frequency scanner searching for the cleanest frequency available. Such scanning can be executed (a) just once during commissioning of the FAP, (b) periodically in regular time intervals or (c) at each power up. Thereby, possible changes in the radio environment could be taken into account by the respective FAP. However, such a solution would result in a frequency assignment being optimal for the respective FAP but not optimal from mobile network point of view.
As has already been mentioned above, known FAPs typically use omni-directional antennas, which radiate (and receive) radio power to (and from) all spatial directions. This allows the FAP to be installed in virtually any place and still allows a reasonable wireless network quality provided to different communication devices.
However, most communication devices that are connected to them tend to create relatively stationary and repetitive propagation conditions as they are not moved around that much. The communication devices could be, for example, personal computers, but one can also think of many other devices that could be equipped with wireless access capability, e.g. home appliances such as a refrigerator, a washing machine and a home alarm system. Most of these devices are stationary and thus situated always in relatively stationary propagation conditions. Even if the devices are mobile, e.g. portable computers, the users tend to use them in only a couple of preferred locations (e.g. table at living room, armchair at bedroom, etc.), also creating relatively stationary and repetitive propagation conditions.
As such there is a large wastage of radio power by the access point as radio power is radiated into areas or locations where there is actually no receiver. Further, a lot of unnecessary interference is created outside the intended zone of radio coverage. As radio power is wasted, the connected communication devices can thus operate at suboptimal conditions only, causing them to have less than best possible quality of service.
In order to improve the radio connection between the wireless access point and the attached communication devices one could think about increasing the transmit power. However, this could result in significant interferences to the other communication devices because the signal will “leak out” of the intended coverage zone.
There may be a need for improving the radio connection between a wireless access point and at least one communication device without increasing the leakage of radio power being transmitted by the wireless access point.